We have previously shown that interferon (IF) alters the structure of the plasma membrane. Furthermore, both Moloney murine leukemia virus and vesicular stomatitis virus (VSV) produced by IF-treated cells have low infectivity. While the content of the G protein (envelope glycoprotein) in VSV produced in IF-treated cells is reduced, no defect in the net charge or molecular weight or the extent of glycosylation and silialyation of the G protein was observed. We have also studied the biosynthesis of the viral proteins (VPs). Although IF inhibits the synthesis of VPs to a varying extent depending on the dose, this inhibition is not likely to be responsible for the reduced incorporation of G protein into the virions since the intracellular VPs accumulated is in vast excess of that incorporated into the virion. The relative rate and extent of glycosylation of intracellulaar G protein in the IF-treated cells are not changed. Glycosylation does not appear to be affected by IF. The decreased amount of G protein in the low infectious virion may be due to blocks in the intracellular transport or utilization of G protein in the packaging of the virion on the plasma membrane.